Wednesday, April 12, 2006

Quicker Solutions?

With gasoline prices climbing back toward $3.00/gallon--and over it in a few areas--the public is growing frustrated by the enormous gap between the paltry measures we can take now to improve fuel economy and the promise of future technological solutions. While inflating tires to the proper pressure and driving more moderately can help a bit, it will take years to move enough hybrid cars into the fleet to change our fuel consumption materially. So, for now, we're stuck; or at least that's the conventional wisdom. An email from a reader started a chain of thought suggesting there might be a practical way we could have a larger impact on the problem without having to wait decades.

You don't have to do much highway driving in urban areas to realize that traffic tends to form waves, with jams bunched up around exits and onramps, and by accidents. This paper by an engineer in the Seattle area describes how this works and explains a scheme he hit on that effectively "cancels the waves." His approach starts with some pretty counter-intuitive notions, including the idea that closing the gap with the car ahead of you, to prevent late merging from other lanes, is one of the worst things you can do when traffic gets heavy. Clearly, his analysis is largely empirical and qualitative, but he makes a good case that some simple changes in driver behavior could reduce or eliminate most traffic jams and allow highways to carry a volume of traffic closer to their designed limits.

Why does this matter, and what does it have to do with high gas prices? Well, as I was reading the article it occurred to me that, although truly major improvements in fuel economy will depend on changes in both consumer preference--fewer large SUVs--and technology--more hybrids and smaller engines--every car on the road already has an impressive efficiency improvement waiting to be unlocked: the difference in mpg between city and highway driving. When cruising at the speed limit, you should achieve close to your car's EPA highway rating, but when you get stuck in stop-and-go traffic, your car is demoted to its city rating, or worse. In the case of the typical sedan, a Toyota Camry, that difference amounts to 10 mpg. For a typical SUV, a Ford Explorer, it's 4-6 mpg. So if we could find a way to eliminate traffic jams entirely, and enable traffic to flow smoothly at a lower speed, we could boost the fuel economy of every car involved by about 40%.

What kind of overall impact would this have? The 2004 Urban Mobility Report of the Texas Transportation Institute at Texas A&M estimated fuel wasted due to traffic congestion at 5.7 billion gallons per year in 2002. That equates to 370,000 barrels/day, or about 4% of total US gasoline consumption. To put that in perspective, all the ethanol used in gasoline in this country only amounts to about 2.5% of the total. Or, looking at it another way, saving the fuel wasted in traffic jams would be the equivalent of putting a couple million hybrid cars on the road.

How can we make this happen? Well, as persuasive as Mr. Beaty's reasoning might be, I'm not convinced that a few "anti-traffic" drivers in each city would be sufficient to eliminate traffic jams, although I'm intrigued by the idea that the highway patrol could achieve the same thing. Nor is it clear how to get millions of people to change their driving behavior in fundamental ways, without changing either laws or some key part of the technology involved, such as the addition of a radio-controlled "idiot light" on the dash, telling us when to speed up or slow down. However, if you've ever driven the New Jersey Turnpike and are among the minority of drivers who pay attention to the system of remotely controlled speed limit signs and traffic warnings, you know how few people slow down when the "Congestion Ahead" sign comes on.

As complicated as traffic seems, the potential energy savings surely justify some investment to go beyond measuring it to actually trying to change the way it flows. And even if the fix requires new technology, or modified road signage, we could see meaningful results from this long before the vast US car fleet turns over enough to make hybrids and other high-mileage vehicles the norm and not the exception. Meanwhile, when you see that constellation of brake lights ahead of you, don't wait until the last second to slow down. Leave a few car lengths and see what happens.

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